1. Field of the Invention
The present invention relates to an ink-jet recording apparatus which performs recording by discharging ink from a recording head to recording medium supported on a platen.
2. Description of the Related Art
As a recording apparatus including a printer, a copy machine and a facsimile which records an image on the recording medium based on image information, an ink-jet recording apparatus is used which discharges ink from a recording head to the recording medium to perform recording. It is essential for the ink-jet recording apparatus to keep constant a gap between the recording head and the recording medium in order to keep high recording image quality since the recording is performed by discharging ink droplets.
If the recording medium of a sheet type such as a sheet of paper is uplifted, the recording head can come into contact with the recording medium to deteriorate or damage image quality. As one method for solving this problem, a platen for attracting a rear surface of the recording medium onto a conveyance surface of the platen by applying a suction force is discussed. Such a platen varies a force attracting the platen depending on characteristics of the recording medium such as stiffness and quality of a material, and further curling which varies depending on ambient humidity.
Normal printing is performed using a margin provided at a surrounding area of the recording medium. However, marginless printing may be also performed. In the marginless printing, the ink discharged from an end edge of the recording media adheres to the platen and then adheres to the recording media again to cause ink spots. Therefore, a marginless recessed section for receiving the ink is provided at a portion of the platen corresponding to the end edge of the recording medium to prevent the ink from adhering to the conveyance surface of the platen and further to prevent generation of the ink spots on the recording medium.
This marginless recessed section is arranged at a plurality of places depending on a size of the recording medium. In such a structure, since a flying length of the ink discharged outside the recording medium up to an impact position becomes long, a part of the ink cannot impact onto the recording medium and becomes floating mist. The mist may contaminate the conveyance surface of the platen, or come around and adhere to a rear surface of the recording medium to cause the ink spots. Therefore, it is discussed that the platen of an attraction type sucks in and collects the ink mist generated in a vicinity of the marginless recessed section by applying a suction force also to the marginless recessed sections.
In the platen of this type, if a single suction force generation unit such as a suction fan simultaneously performs attraction of the recording medium and suction at a suction collection section (marginless recessed section), when an attraction force is varied according to a type of the recording medium, a suction wind velocity generated in the suction collection section is also varied. Accordingly, when the suction wind velocity is low at the suction collection section, the floating mist can come around and adhere to the rear surface of the recording medium to cause the ink spots. When the suction wind velocity is high, the ink which otherwise should impact on a vicinity of an end portion of the recording medium is flown over to an outside of the recording medium to deteriorate the image quality.
Thus, it is demanded that, while the recording medium is attracted by the appropriate suction force, the suction force having a desired suction wind velocity is applied into the suction collection section outside the recording medium. In order to meet this demand, Japanese Patent Application Laid-Open No. 2005-205650 discusses a structure in which the suction force is applied by a dedicated suction force generation unit to the suction-collection section outside the recording medium.
However, if the suction wind velocity is decreased at the suction-collection section outside the recording medium, the suction force at an inner suction-collection section covered with the recording medium becomes insufficient. More specifically, the recording medium into which the ink infiltrates gets wet and swollen, and starts to become extended (cockling). Since the extension is concentrated on the inner suction-collection section of the recording medium having a weak suction force, the recording medium is uplifted at the inner suction-collection section in a vertical direction.
If the recording medium is uplifted, the impacting accuracy of the ink is decreased to deteriorate the image quality, and the recording medium may come into contact with the recording head (which is referred to as uneven cockling). On the other hand, if the suction force at the inner suction collection section covered with the recording medium is increased, the suction wind velocity at the suction-collection section outside the recording medium is also increased. Thus, the ink which otherwise should impact on the vicinity of the end portion of the recording medium is flown away by the suction force, thereby deteriorating the image quality.